1. Field of the Invention
The present invention pertains to heart valve prostheses and in particular, to bileaflet heart valve prostheses using pivotable valve members.
2. Description of Related Art
Various types of heart valve prostheses have been proposed, and many give generally satisfactory operation and have lifetimes longer than the life expectancy of the patient who is to wear the prosthesis. One popular design for a heart valve prosthesis included an annular valve body in which a pair of opposed leaflet occluders are pivotally mounted. The occluders are movable between a closed, mated position so as to block blood flow in an upstream direction, and an open position allowing blood flow in a downstream direction.
Several improvements to heart valve prostheses are still desired. For example, in order to reduce assembly costs and in order to minimize any difficulties arising from variations in assembly techniques, it is desirable to provide leaflet occluders which may be fitted to the valve body by temporarily distorting the leaflet occluders so as to permit their snap-in engagement within recesses formed in the valve body. Once installed, it is particularly desirable that the leaflet occluders be free to move within the valve body with minimal friction.
Also, it is particularly desirable that a heart valve prosthesis be provided which suffers no appreciable change in operating efficiency, at least over the life of a patient wearing the prosthesis.
In another area of potential improvement, it is desirable to impart a more rapid closing time to the leaflet occluders so as to reduce regurgitation. However, such quickening of the closing time should not be accompanied by an increase of frictional wear of the leaflet mounting parts, even if such increased wear results only in relatively minor aberrations of the occluder movement.
Further, although it is desirable to have closing time as rapid as possible, this should not be accompanied by an increase in noise during operation of the prosthesis, for example, as the leaflet occluders engage the valve body as they seat there against to block any regurgitation that might otherwise occur.
In a bi-leaflet type of heart valve prosthesis, the leaflet occluders typically engage each other along diametral edges, and engage portions of the valve body at points remote from the diametral edges. Such engagement should not give rise to clicking or other such noises, even though the closing time thereof is significantly shortened.
Also, any rebounding of the leaflets should be controlled so as to prevent any unnecessary wear, and also to conserve hemodynamic energy which operates the prosthesis. In particular, it is important that any decreases in valve closing time do not contribute to rebounding of the leaflets, as might otherwise be expected.
In the past, leaflet occluders have occasionally been slightly undersized so as to allow a purging blood flow therearound, even when the leaflets are closed. Such flows wash over localized, edge surfaces of the leaflets and the valve body to prevent any clotting that might occur at those locations. It is important, however, that hemodynamic energy of a patient be conserved as much as possible and accordingly it is important that the amount of undersizing of the leaflet occluders be accurately controlled. Such sizing, of course, depends upon manufacturing tolerances in the valve body as well as those of the leaflet occluders. Due to concerns with respect to manufacturing costs, which are directly related to manufacturing tolerances, alternative arrangements for providing a purging flow around the leaflet occluders, particularly at their hinged connections to the valve body, in a manner which conserves hemodynamic energy, is still being sought after.